Ant possible cause for this?

Why would a man (who is a 'friend',more like an aquaintance), who has been ignoring me and being so serious towards me, suddenly finding an interest in me when he realized I have made some accomplishment? I've known him for 5 yrs. At the beginning he was courteous and and talkative towards me. Then suddenly, he became cold and being awkwardness round me. Only his wife is nice towards me. When I am around he gets quiet and seem angry. But I know that I do did not do anything to him, except for an occasional "no thanks" if he asked to help me. But he is normally outgoing and talkative (ALPHA MALE). But with me, he seems out of place and serious. If I need to ask him anything, I get uncomfortable, because of his demeanor. He looks at me almost with his eyes closed. I notice I am the only one in the group he treats like this. Anyway, I was shocked to see his sudden interest in something that I am accomplishing now. But yet, he is still weird around me. IF he is front of me talking to me or listening to me, he is looking at me sideways which I think is rude, and quit strange since he is directly in front of me.
(still afraid to ask him why)

Sounds to me like he's got a thing for you, but is absolutely intent on respecting his marriage, so he's trying to maintain a distance and not create any opportunity to hurt his wife. I'd respect that.